Lin Chou Cheng wrote a tutorial on ‘Silhouette modeling’. We republished it here with his permission. You will find the original on his website.
This article is aimed to equip you with a better informed overview when constructing a 3D base mesh for games with the technique of Object Space Normal Mapping. In the art of digital model making, there are many different methods that let you manually shape the polygons according to your liking. For instance, these methods are box modelling, edge modelling, image-based modelling (e.g., like the displacement map technique), digital sculpting and etc. You can read more about these techniques here if you are new to 3D modeling.
Though some of the above methods did warrant you some creative freedom during the process of meshing, however, not all the methods are efficient when there is a strict requirement for you to model after a reference with precision. Therefore, I would like to share with you an alternate approach, which might be handy to you when building something that required high-level of exactness. The technique that I am about to discuss here was largely originated from the good old fine art of Silhouette Paper-Cut, as shown in the following screen grabs. You can read more about the used of Silhouette as an art form via Wikipedia if you are curious about it.
Anyway, should you ever trace the etymology and the origins of Silhouette, you will discover that the concept of silhouette originated mainly with anything that had to be done or made cheaply! In fact, such historical backdrop does coincide to our heuristics when making video game art, where everything we develop is bounded to some form of limitations, be it polygon count or texture resolution, and we ought to make things look great out of the cheap! Although having said so, Silhouette is an important visual property in design communication, whereby its positive and negative shape can really help us to be better at recognizing the visual information that presented before us. Sometimes, silhouette can be used to bedazzle us too, as demonstrated in the following examples:
Samples of Silhouette illusion like apple face woman
From the perspective of science and facial recognition studies, the research conducted by the Stanford University had highlighted that the appropriate used of silhouettes had helped humans to extract accurate information (ScienceDaily, 2007). Therefore, it is a norm for all the learned concept artists to first explore their design in a series of black & white thumbnails before dressing it up with layers of complexities.
So, what does it got to do with our process of digital model making then?
Well, we can actually borrow the technique of Silhouette Paper Cutting to build a nearly perfect game mesh whenever there is a good sideview reference being provided. If there isn’t one (this happened all the time in a low-budget production), then you ought to draw or make one from the solely available perspective-visual.
To adapt from the practice of silhouette paper cutting into digital model making, we are not going to cut any papers in our 3D viewport. Instead, we are going to trace a polygonal plane that being texture-mapped with silhouette information. The referred “tracing” is actually an act of splitting the polygon plane along the outline of the silhouette. This split polygon action can be easily carryout with some Edit Mesh toolset that is commonly found in all 3D applications. For instance, in Autodesk Maya, we could use the Interactive Split Tool, the Classic Split Tool, or the new Multi-Cut Tool for performing this action. In order to give you a better sense about this technique that I was talking about, let’s take a look at the following production breakdown, which I had documented at my end.
The Making of Tulèk: a machete for TRoLLING AGE
Prior to the making of anything, it is crucial for you to have a dependable concept art or construction drawing that derived from a production style guide. However, for this showpiece, I only used a string of keywords to guide the development of this fictional machete. The keywords that I have used were Shotel, Turkish Scimitar, Tuareg, Machete, Golok, Magic Rune, Celtic, La Tune. (For students, do not follow what I do here.)
Tulek fantasy celtic magical machete weapon design concept
As I have mentioned earlier, the method that I am about to demonstrate here was originated from the idea of silhouette cutting. Therefore, to use this method effectively, you need to get the silhouette of your target object readied beforehand, and the best place to source for the silhouette of your object is to look at its side profile. For instance, in the making of Tulèk, I have created the silhouette of this machete with just few clicks in Adobe Photoshop, as the side profile of my line art was crisp enough.
However, in some other productions, you don’t always get a cleanly drawn concept art that is suitable for modelling used. There will be a time where the only given reference is just a photograph (which is awfully captured). Then, you will have no choice but to learn to be resourceful and retouch whatever you had in Adobe Photoshop, or manually draft the side profile-view that you need. Should you have been given a good side-view reference, then do what I have did by directly mapping the line art drawing straight onto a polygon plane in Maya (as demonstrated in the following figure). Now, with everything in place, you can begin to trace the outline of your object in an orthographic sideview. To trace after the silhouette, there are two operational options for you to choose from:
Option A – using the Split-Cutting tools
To go by this option, first, you would need to divide the polygon plane into a series of grids with the insert edge loop function. Then, you can either use the interactive or the classic split tool to anchor new edges that flow according to outline of your object. You can tryout the new Multi-cut Tool in Maya, as it is quite reliable. Lastly, after you done with tracing, do delete all the negative spaces that surrounding the outline, and you are done for step one.
Option B – using the Create Polygon tool
In this option, the Create Polygon tool will enable you to create a whole new polygon plane that matches the outline of your reference plane. The Create Polygon tool would function by connecting all the vertices that you had laid upon. It is a powerful abstraction tool that can support you to create a clean 2D shape.
Options for tracing a silhouette outline in Autodesk Maya
No matter which option you used, our main objective here is to obtain a planar-poly plane that is closely resembling to the silhouette of your target reference. This planar-poly plane is expected to be a N-GON momentarily.
In the next step, it is all about “connecting the dots” by using either the Interactive Split tool or the Multi-
Cut tool to fuse the vertices and form the quads (see 2 in the following figure). During this step, you are expected to insert more edges for smoothing out the entire 2D poly-shape that you have cut earlier, and do keep all the poly-faces in quads (or 4-sided) and avoid triangulation.
Insert edge loop with connecting the dots
During the process of “connecting the dots”, this is also the best time for you to forge the topological flow of your model. For instance, in the making of Tulèk, I have spent considerable amount of time in adjusting the spacing between each edge loop, while busy sowing loops of edges onto the 2D poly-plane, so that I could elevate the blade’s body with the extrude function later. In this phase, you can choose to temporary omit out parts like the hilt (or the handle) of the machete like what I did in step 3 (see above).
After you’re done defining the shape of the model, you are advised to punch out the details (esp. holes), which required by the design of the blade. For instance, in Tulèk, I have cut out the serrations and the loop-guard area of the handle before I proceed to extrude the body of the blade (see 4 in the following figure).
Detailing for 3D machete with serration
After several rounds of extrusion, the form of my machete has started to look more solid as the thickness of its body has added some sense of weight to it. You do not need to optimise the polygon count of your base mesh yet at this stage. The reason is simply because this base mesh is meant to be duplicated and “upgraded” into a hi-res version that carries all the finest details. The hi-res version of Tulèk is meant to be used for generating Object Space Normal Map for us. To craft a hi-res model that has the realistic quality, you would need to apply the function of smoothing at some stage. In order to fully utilise the function of smoothing, it is advisable for you to keep everything in quads if you want to have good result. In addition to that, a base mesh that kept in quads is usually much more easy to be upgraded with details if compare to a triangulated model. With such reasoning, this is why I have kept quite a lot of edge loops for the mesh, especially the serrated part of the machete (See 5). Again, do not worry about the polygon count at this stage, we can always optimize the base mesh at the final stage even after texturing.
All the while, I have been working on a single side of Tulèk. It is about time for me to make it into a complete mesh. Therefore, I have mirrored the machete, and then combined them into one solid mesh with all vertices being merged. After that, I have started to work on the handle of Tulèk and shaped it into a hammer (See 6 & 7). It took me quite some time to shape the handle of the machete, as it had much rounded form versus the edgy looking body-blade.
Constructing a hammer handle for a machete in 3D
Lastly, with everything in place, it is a standard routine to make sure your base mesh is free from any topological errors. If you are not sure how to detect the topology errors that your base mesh might have, then I would suggest you to visit this article, “How to detect topology error in polygon mesh?”.
And, that’s all about this technique which I wanted to share with you. Hopefully, through this article, you get to gain some creative confidence in how easy it is to build a solid base mesh and a sword-like weapon. Also, should this method being automated, then you shall have the feature that similar to Shadowbox that found in Zbrush. Go read more about it if you are interested.
In order to lend you one more final support, I have loaded Tulèk into Sketchfab for you to reference the topological flow of the mesh. Simply click on the following window, the mesh shall be loaded in real-time. If you are a 3D artisan and do not have a Sketchfab account yet, then I would strongly recommend you to get yourself a Sketchfab account now!
Thanks Lin Chou!
You will find more of Lin Chou’s tutorials on www.gameartworkbook.com.